1. Field of the Invention
The present invention generally relates to detection of organic and inorganic contaminants, and more particularly to the analysis of water supplies for the measurement and characterization of organic and inorganic contaminants therein. In particular, this invention relates to devices and methods for measuring cumulative dissolved solute fluxes and cumulative fluid fluxes in flow systems. The term flow systems as used herein includes, but is not limited to, saturated and variably saturated geologic and nongeologic media, such as saturated and unsaturated soils, sediments and aquifers.
2. Description of the Relevant Art
The presence of contaminants in ground water supplies and other water resources can present significant pollution problems. A wide variety of organic and inorganic contaminants may be present in subsurface, water-bearing geologic formations, depending on how the overlying land under consideration has been used. For example, many different organic solvents and related compounds (e.g., non-halogenated and halogenated organic compounds) may exist in groundwater supplies beneath factory sites and other locations where extensive use of these chemicals has occurred over long time periods or accidental spills or inappropriate disposal have occurred. Of particular concern are halogenated (e.g., chlorinated) solvents including perchloroethene (PCE), trichloroethene (TCE), dichloroethane (DCA), vinyl chloride (VC), methylene chloride (MC), and others. However, in addition to halogenated solvents, a wide variety of other organic compounds shall be encompassed within the term xe2x80x9corganic contaminantsxe2x80x9d as discussed below. Of equal concern is the presence of benzene, toluene, xylenes, and other constituents of petroleum-based fuels (e.g., jet fuel, gasoline, diesel fuel, and the like) in waste-bearing geologic formations underlying various transportation-related facilities. Examples of such facilities include gasoline stations, airports, military bases, and the like. Other contaminants of various pesticides and nutrients used in crop production or suburban lawns and gardens or golf courses; and trace metals such as arsenic and chromium and the like used in industrial operations. At many sites, both organic and inorganic contaminants may be found as mixtures. A contaminant group designated as polyaromatic hydrocarbons (PAHs), such as naphthalene, phenanthene, anthracene, benzo-a-pyrene and others, are constituents of coal and/or tars and creosote found at former gas manufacturing sites and wood treating facilities. Regardless of the particular contaminants of concern, the presence of these chemicals at or near subsurface or surface water supplies is a considerable public health concern and of ecological significance. Accordingly, the present invention shall not be restricted to the monitoring of any given organic or inorganic compounds.
Several methods have been used to analyze water quality. Of particular importance is the analysis of groundwater existing in aquifers for concentrations of organic waste products. The term xe2x80x9caquiferxe2x80x9d as used herein describes a large water-bearing geologic formation that is capable of yielding sufficient water to satisfy a particular demand (e.g., drinking water or industrial uses or irrigation needs). Prior testing methods have involved the drilling of wells directly into the aquifer, followed by the placement of screening materials within the wells. For deep aquifers, dedicated submersible pumps are then positioned in each well to withdraw numerous water samples of delivery to the well head. For shallow aquifers, bailing the water or pumping from above ground can be used for sampling. Thereafter, the samples are analyzed to determine the type and concentration of organic contaminants in the collected water samples. Measurement of water levels (or pressure) in a network of wells enables estimation of average fluid fluxes, if the hydraulic conductivity of transmitting of the aquifer is known.
While the prior methods provided important information regarding the levels of contamination in the water supplies of concern, they did not allow the estimation of contaminant fluxes and fluid flow fluxes. Although prior methods and apparatus are capable of measuring instantaneous fluid fluxes, no direct methods exist that permit simultaneous measurement of horizontal cumulative solute mass flux and the cumulative fluid flux in either saturated or variably saturated flow systems. Pan lysimeters (free drainage samplers) and suction lysimeters have both been used to measure cumulative fluid and dissolved solute fluxes when the direction of flow is vertical; however these technology are not suitable for measuring horizontal fluxes. Thus, to simultaneously measure cumulative fluid fluxes or cumulative dissolved solute fluxes in multiple directions associated with one or more fluids flowing in flow systems, a new method is needed.
Current methods for estimating contaminant mass flux (J) in aquifers are made from independent instantaneous measurements of flux (q) and solute concentration (C) in the pore water. Several methods exist for measuring q and C in saturated and unsaturated geologic formations. All existing methods are confined to providing estimates characterized over vertical or horizontal sampling lengths. For example, in cases of horizontal saturated flow, q and C are estimated over isolated vertical segments of a well; whereas, in estimating solute mass and fluid fluxes associated with vertical infiltration or leaching, the pertinent sampling lengths are the horizontal or areal extents of infiltration. Continuous temporal measurements of q can be done for saturated flow systems. Methods of measuring vertical unsaturated flow require that the flow be intercepted and then retained for direct volumetric measurement and chemical analysis. Thus, there is a method for estimating vertical cumulative water fluxes.
Solute concentrations (C) are usually measured at discrete moments in time in both saturated and unsaturated flow systems. No methods exist to measure cumulative solute fluxes for saturated flow systems. However, a device exists to intercept vertical unsaturated flow. Chemical analysis of the water intercepted by this device could be used to estimate cumulative dissolved solutes transported as a result of vertical fluid flow. Measured q and C are used as shown in the following equation to estimate the instantaneous contaminant flux, J.
J=qxc2x7Cxe2x80x83xe2x80x83(1)
Equation (1) is assumed to characterize contaminant mass flux over a specified sampling dimensions (i.e., an isolated vertical segment of a monitoring well) and for a reported sampling time. For geologic media, this approach of characterizing contaminant fluxes is subject to significant experimental and conceptual errors. Consider first, that the specific discharge, q (the magnitude and the direction) and solute concentration, (C) are both functions of position and time. This suggests that the magnitude and the direction of mass flux, J, also vary with position and time. Thus, any sampling of q and C over an isolated vertical or horizontal length precludes accurate local estimation of the magnitude and the direction of both fluid and contaminant fluxes. Second, the short-term sampling procedures often used to obtain C and q preclude estimation of the time-integrated (i.e., cumulative) values for fluid and contaminant fluxes. Such time-integrated contaminant fluxes are useful for assessing health risks associated with groundwater contamination, for assessing the direction and mass flow of contamination leaving a compliance boundary, for assessing the total amount of off-site contamination contributed by one or more sources, and for assessing the benefits of removing or remediating sources of subsurface contamination. Finally, because the above equation uses spatially-averaged values of q and C it does not produce valid estimates of contaminant fluxes in typically heterogeneous aquifers or vadose-zone flow systems. Accurate estimate of length-averaged contaminant fluxes, are obtained only from the direct spatial integration of measured local contaminant fluxes, J. Thus, existing methods for measuring q and C do not provide adequate discrete or time-integrated estimates of contaminant fluxes in saturated or variably saturated geologic formations.
Traditional testing methods also require a large amount of expensive equipment, are labor intensive, and involve complex operating procedures. Moreover, conventional monitoring techniques which require the removal of numerous fluid samples for individual testing typically generate large quantities of waste products (e.g., residual sample materials) which, if sufficiently contaminated, can present significant disposal problems. Prior to development of the present invention, a need therefore remained for an efficient testing system which avoids these disadvantages and enables ground water supplies (as well as surface water sources) to be tested in an accurate, rapid, and effective manner.
The claimed invention represents a unique and highly-efficient alternative to the methods listed above. It does not require extensive equipment (e.g., submersible pumps) and complex operating procedures. The invented device can be used to analyze large water supplies without extracting any contaminated liquid sample materials so that with disposal of generated waste fluids, problems are avoided. The invented device can be used to obtain continous estimates of the magnitude and direction of both fluid and dissolved solute fluxes over a specified sampling length (i.e. over an isolated section of monitoring well). Finally, the method and apparatus described below enable the water supply of interest to be simultaneously analyzed at multiple locations so that the contamination may be xe2x80x9cmappedxe2x80x9d enabling spatial delineation of the areas of concern. Decontamination of the water source can then occur in a more site-specific and accurate manner. The present invention therefore involves a highly effective testing system which represents a substantial advance in the art of contaminant detection and remediation as discussed further below.
It is an object of the present invention to provide a highly efficient testing method and apparatus which enables the quantitative and qualitative analysis of contaminants in a flow system.
It is another object of the invention to provide a method and a device for capturing a representative concentration of contaminants in a flow system which allows the analysis of a wide variety of different organic and inorganic materials at varying levels.
It is another object of the invention to provide a method and apparatus for monitoring contaminants in a flow system which uses an operating system and procedure of minimal complexity.
It is another object of the invention to provide a method and apparatus for monitoring contaminants in a flow system which avoids the need for pump systems.
It is a further object of the invention to provide a method and apparatus for monitoring contaminants in a flow system which enables testing to take place without physically removing any water samples from the test area.
It is an even further object of the invention to provide a method and apparatus for monitoring contaminants in water supplies which avoids the generation of waste products (e.g., residual sample materials), and likewise eliminates the disposal problems associated therewith.
Another object of the invention is to provide a method and apparatus for monitoring contaminants in a flow system which is characterized by reduced labor requirements and processing times.
It is a still further object of the invention to provide a method and apparatus for monitoring contaminants in water supplied which enables a spatial distribution (e.g., a vertical or horizontal analysis) of the contaminants to be obtained.
It is a still further object of the invention to provide a method and apparatus for monitoring fluids and contaminants and their associated local fluxes in water supplies which facilitates the mapping of contamination zones in a highly effective manner so that site-specific, high-efficiency remediation procedures may be initiated.
It is a still further object of the invention to provide a method and apparatus for monitoring fluids and contaminants and their associated local fluxes in water supplies to facilitate an assessment of the direction and mass flow of contamination leaving a compliance boundary.
It is a still further object of the invention to provide a method and apparatus for monitoring fluids and contaminants and their associated local fluxes in water supplies to facilitate an assessment of the total amount of off-site contamination contributed by one or more sources.
Another object of the invention is to provide a device and method for measuring the following at specific locations in a fluid flow system:
1) Directions and magnitudes of local cumulative fluxes of multiple fluid flows, and
2) Directions and magnitudes of local cumulative solute mass fluxes associated with these fluid flows.
Finally, another object of the invention is to provide a device and method of measuring the following at specific locations a flow system:
1) Directions and magnitudes of local cumulative water fluxes, and
2) Directions and magnitudes of local cumulative solute mass fluxes for solutes associated with the fluid flow.
In accordance with the foregoing, the invention involves both a system and a method that uses a permeable unit designed to simultaneously measure local cumulative dissolved solute fluxes and fluid fluxes when placed within a fluid flow system. As used herein, xe2x80x9cfluid flowxe2x80x9d can be, but is not limited to, groundwater or other fluids flowing in a porous medium such as a geologic formation (rock, soil, clay, and like materials). Typically, fluids within flow systems contain dissolved constituents, including organic and/or inorganic contaminants of concern.
The monitoring device of the present invention comprises a self-contained permeable unit that will intercept fluids and allow the fluids to flow through the unit, but not retain these fluids. The interior of the permeable unit contains at least one matrix of hydrophobic and hydrophilic permeable and insoluble sorbents that are capable of retaining dissolved organic and/or inorganic solutes present in fluid intercepted by the permeable unit. The sorbing matrix can also be impregnated with known amounts of fluid-soluble tracers; these tracers are used to estimate total fluid flux through the permeable unit. The selection of sorbent matrices to be used with the device could be, but need not be limited to porous pellets, fibers, or stabilized liquids or gels. The sorbent matrix or matrices that are packed within the permeable unit could have the inherent capacity to selectively sorb contaminants from the fluid flow or in the alternative, the matrix can be coated or impregnated with specific sorbents that are selected to absorb or adsorb specific contaminants.